The present invention relates to fiber-optic communication systems, and more particularly, to ways in which to monitor and control the operating temperature of optical detector components for use in fiber-optic communications systems.
Fiber-optic communications systems typically use optical amplifiers to amplify optical signals that have traveled over multi-kilometer fiber-optic transmission links. A typical optical amplifier may be based on fiber that has been doped with rare-earth elements such as erbium. Fiber amplifiers are typically pumped by diode lasers.
Because the gain spectra of erbium-doped fiber varies as a function of temperature, erbium-doped fiber amplifier coils are sometimes temperature stabilized by heating them to an elevated temperature. A fiber amplifier may be designed to operate within a temperature range of 0 to 70xc2x0 C. Temperature-stabilization schemes have generally used heaters that maintain fiber amplifiers at the maximum temperature in the fiber amplifier""s operating range (i.e., at 70xc2x0 C.). If the environmental temperature falls below the maximum operating temperature, such a heater can be used to ensure that the temperature of the doped fiber coil is maintained at the maximum temperature. This ensures temperature stability and prevents drift in the spectral characteristics of the fiber amplifier""s gain.
In addition to the fiber coil, other components of the optical communication system may be sensitive to temperature changes. For example, components of an optical detector, such as a photodiode and a transimpedance amplifier, may be affected by temperature changes. The transimpedance amplifier may be configured to produce a relatively low output voltage (e.g., 0-500 mV). This low voltage may be amplified to a relatively high voltage level (e.g., 0-5 V) by a gain stage. The gain stage may be external to the transimpedance amplifier or may be internal to the transimpedance amplifier. The gain stage (whether internal or external) may also be affected by the temperature changes that influence the operation of the photodetector.
It is therefore an object of the present invention to ensure temperature stability of an optical detector in a fiber-optic communication system and prevent drift in the spectral characteristics of the detector""s gain.
It is also an object of the present invention to provide ways in which to monitor and control the temperature of optical detector components in a fiber-optic communication system.
These and other objects of the invention are accomplished in accordance with the principles of the present invention by providing a housing that allows optical detector components to be maintained at stable temperatures during operation. The optical detector components may be stabilized at relatively low temperatures to improve performance. As an example, the optical detector components may be temperature-stabilized at about room temperature. Of course, the optical detector components may be stabilized at other temperatures that improve the performance of the detector components or the overall performance of devices within the housing.
According to one exemplary embodiment, the optical detector may be provided in an optical amplifier module. The optical detector may be used to monitor an optical signal input to and/or output from the optical amplifier. The output of the optical detector may be used to control a pump laser for a doped fiber coil used for optical amplification. The optical detector may include a photodiode (such as a PIN diode) and a transimpedance amplifier. The photodiode and/or the transimpedance amplifier may be provided in a temperature-controlled housing that maintains the components at a stable operating temperature. One or more additional components of the amplifier module, such as the doped fiber coil, may be provided in the temperature-controlled housing as well.
The transimpedance amplifier may be configured to produce a relatively low output voltage (e.g., 0-500 mV). This low voltage may be amplified to a relatively high voltage level (e.g., 0-5 V) by a gain stage. The gain stage may be external to the transimpedance amplifier or may be internal to the transimpedance amplifier. The gain stage (whether internal or external) may also be affected by the temperature changes that influence the operation of the photodetector. Accordingly, the gain stage may also be provided in a temperature-controlled housing.
The temperature-controlled housing may include insulation to help ensure that proper temperatures are maintained. When proper insulation is provided elsewhere in the amplifier module or other optical network module in which the components are used or when less critical temperature control capabilities are acceptable, the components that are to be temperature controlled may be mounted directly to a thermoelectric cooling element or other temperature controller without using a housing.
According to a further exemplary embodiment, the optical detector may be provided at a network node, for example, as part of an optical receiver for the optical transmission signal. The optical receiver may include, for example, a demultiplexer, a photodiode, a transimpedance amplifier, an analog-to-digital converter, and a temperature-controlled housing. The temperature-controlled housing may house the photodiode and/or the transimpedance amplifier, among other components, to maintain the housed equipment at a stable operating temperature.
The temperature-controlled housing may be constructed using thermally-insulating materials such as fiberglass, foam, plastic, or any other suitable insulating packaging. Copper or other suitable thermally-conductive materials may be used to distribute heat within the housing. Thermo-electric cooling elements may be used to control the temperature of the housing. The thermo-electric cooling elements may be placed between, for example, a plate of copper within the housing and a heat sink that is external to the housing. The optical detector components may be placed in the vicinity of the copper plate. Ports may be provided through the housing to permit signals to pass into and out of the housing.
The temperature within the housing may be monitored using a temperature sensor based on a thermocouple, a temperature-sensitive resistor, or any other suitable temperature-sensitive element. A local control unit in the fiber amplifier may be used to control the temperature of the thermo-electric cooling units. If the local environmental temperature falls below the temperature set point for the housing, the thermo-electric cooling units may be used to heat the housing. If the local environmental temperature rises above the temperature set point for the housing, the thermo-electric cooling units may be used to cool the housing.
Information on the temperature of the housing that is monitored using the temperature sensor may also be provided to remote monitoring locations. For example, the temperature information may be provided to a central office. A network management facility may gather information such as the information on the temperature of the optical amplifier housing and may, if desired, control the operation of the housing and other fiber-amplifier operations remotely.
Further features of the invention and its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.